Every alkane name — however long — comes from the same five-step recipe applied in order.
The whole game: locate the parent chain, then attach and number the branches. Structures drawn live.
1. Find and Name the Longest Continuous Chain (the Parent)
The longest unbroken path of carbons is the parent chain, and its length sets the base name (methane, ethane, propane, butane, pentane, hexane…).
The trap: the longest chain can turn a corner, so trace every branch as a possible chain end before committing.
2. Number the Chain to Give Substituents the Lowest Locants
Number from whichever end gives the branches the smallest position numbers (locants), so the structure below is 2-methylpentane, not 4-methylpentane.
3. Name Each Branch as an Alkyl Substituent
Name a branch for its own carbon count with an -yl ending — methyl, ethyl, propyl — plus a locant for the parent carbon it hangs from.
A three-carbon branch joined through its middle carbon is isopropyl.
4. Alphabetize and Assemble the Full Name
List substituents alphabetically by base name, collapse repeats with di-/tri- multipliers (ignored when alphabetizing), and punctuate with hyphens (number–word) and commas (number,number).
5. Rings Get "Cyclo-" — and May Be the Parent
A ring takes the cyclo- prefix, and a single ring substituent needs no locant, so methyl on a six-ring is simply methylcyclohexane.
Whichever holds more carbons — ring or chain — becomes the parent.
6. Summary
Longest chain = parent · number for lowest locants · name branches as alkyl groups · alphabetize (ignore di-/tri-) · cyclo- for rings, bigger piece wins.
Quiz yourself
Tap a question to reveal the answer — free, no login.
2-Methylpentane. The parent is pentane (5 C in the longest chain), and numbering from the near end puts the methyl on C-2 rather than C-4.
Substituents are listed alphabetically by their base name, and "ethyl" comes before "methyl." Locants follow the substituents; they don't change the alphabetical order.
No. Multiplying prefixes (di-, tri-, tetra-) are ignored for alphabetizing, so "dimethyl" is sorted under "m." It still appears in the finished name, e.g. 2,3-dimethylbutane.
Ethylcyclohexane. With a single substituent on a ring, every position is equivalent, so no locant is needed. The ring (6 C) beats the ethyl (2 C), so it is the parent.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.